Associate Professor, Department of Philosophy, Lewis & Clark College

Max Black on Identity of Indiscernibles; or Who is Castor and Who is Pollux?

Added on by jay odenbaugh.

Consider the following two principles, the Identity of Indiscernibles and Indiscernability of Identicals.  

Max Black

Max Black

For any property F, if object x has F just in case y has F, then x = y. 

For any objects x and y, if x = y, then x has F just in case x has F. 

The second principle is trivial but the first is not. Could an object x and an object y has all of the same intrinsic and extrinsic properties and yet be distinct? Consider the following argument that the Identity of Indiscernibles is false. 

  1. Suppose the universe contains two perfectly symmetric iron spheres two miles apart which have all the same intrinsic and relational properties and there is nothing else. 
  2. It follows that the two spheres possess the same properties and hence are indistinguishable. 
  3. However, they are not identical. 
  4. Hence, indiscernibles may not be identical.

Question: Do you agree with the premises? If not, which premise(s) do you reject?